NED Abstract

Copyright by European Southern Observatory (ESO).
Reproduced by permission
2005A&A...438..507B
Lopsided spiral galaxies: evidence for gas accretion
F. Bournaud, F. Combes, C. J. Jog and I. Puerari
Received 3 January 2005 / Accepted 15 March 2005
We quantify the degree of lopsidedness for a sample of 149 galaxies
observed in the near-infrared from the OSUBGS sample, and try to
explain the physical origin of the observed disk lopsidedness. We
confirm previous studies, but for a larger sample, that a large
fraction of galaxies have significant lopsidedness in their stellar
disks, measured as the Fourier amplitude of the m=1 component
normalised to the average or m=0 component in the surface density.
Late-type galaxies are found to be more lopsided, while the presence of
m=2 spiral arms and bars is correlated with disk lopsidedness. We also
show that the m=1 amplitude is uncorrelated with the presence of
companions. Numerical simulations were carried out to study the
generation of m=1 via different processes: galaxy tidal encounters,
galaxy mergers, and external gas accretion with subsequent star
formation. These simulations show that galaxy interactions and mergers
can trigger strong lopsidedness, but do not explain several independent
statistical properties of observed galaxies. To explain all the
observational results, it is required that a large fraction of
lopsidedness results from cosmological accretion of gas on galactic
disks, which can create strongly lopsided disks when this accretion is
asymmetrical enough.